As an example of existing literature, Japanese Unexamined Patent Application Publication No. 2008-27736 (PTL 1) discloses a backlight unit in which a light guide can be securely fixed to a chassis regardless of a change in temperature conditions. In the backlight unit described in PTL 1, a rectangular metal frame supports light emitting diodes (LEDs) and holds the light guide. The LEDs are attached to a side wall of the metal frame.
The metal frame is equipped with long-side ribs, which protrude from one long-side wall toward the opposite long-side wall, and a short-side rib, which protrudes from one short-side wall toward the opposite short-side wall. The long-side ribs and the short-side rib are attached to the metal frame such that they have spring characteristics. The long-side ribs press the light guide against the opposite long-side wall. The short-side rib presses the light guide against the opposite short-side wall.